The present invention relates to apparatus for controlling an actuator in response to movement of a control member, and in particular to apparatus for sensing the position of a member, such as a control member for an actuator, through use of light guides such as optical fibers.
There are various situations in which it is desirable or necessary that a manual control member be located remote from, and electrically isolated from, the actuator which it controls. So-called "cherry pickers" used by utility companies to lift workers to overhead power lines are examples of such equipment. Conventionally, the cherry picker is mounted on a truck, and consists of a basket attached to the end of a boom. Control levers in the basket control actuators at the base of the boom. The actuators are operable to extend or retract, elevate or lower, and pivot the boom. It is desirable that the manual controls located in the basket be electrically isolated from the ground so that accidental contact with the overhead power lines will not result in grounding of the power line and electrocution of the worker in the basket.
U.S. Pat. No. 4,044,856 (Stevenson) discloses lifting equipment of the "cherry picker" variety, wherein fiber optics are used to control the actuators. Specifically, light signals are used to indicate the positions of the manual control levers. The light signals are communicated back to the base of the boom over optical fiber light guides. At the base of the boom, the light signals are detected and used to control the operation of the actuators. Electrical isolation between the manual control levers and the controlled actuators is assured because each manual control lever is coupled to the controlled actuator only by light guides, which are not themselves electrically conductive.
U.S. Pat. No. 4,044,856 describes a number of arrangements by which the light signals can be controlled by operation of the manual control levers. Other arrangements for controlling light signals in accordance with the position of a movable member are described in U.S. Pat. No. 4,249,076 (Bergstrom et al.). Neither patent describes an arrangement wherein a single light signal is used to indicate deflection of a control lever or other movable member by variable amounts in two different directions.